Sound-attenuating housing

ABSTRACT

Sound-attenuating housing ( 10 ) for a heat pump ( 34 ) comprises a base chassis ( 11 ), a first sub-chassis ( 17 ) and a second sub-chassis ( 19 ). The base chassis ( 11 ) is surrounded by upstanding walls ( 12 - 15 ) and has a top ( 16 ) adapted to engage with the upstanding walls ( 12 - 15 ), thereby to form an enclosure for the heat pump ( 34 ). The first sub-chassis ( 17 ) is provided within the enclosure, and is mounted on the base chassis ( 11 ) via-anti-vibration mounts ( 18 ). The second subchassis ( 19 ) is provided within the enclosure, and is mounted on the first sub-chassis ( 17 ) via anti-vibration mounts ( 21 ). The second sub-chassis ( 19 ) forms a mounting surface for a heat pump compressor ( 25 ), whilst the first sub-chassis ( 17 ) forms a mounting surface for other components of the heat pump ( 34 ).

This invention relates to sound-attenuating housing. In particular, it relates to sound-attenuating housing for a heat pump.

A heat pump in its simplest form comprises a closed circuit around which a refrigerant fluid is circulated. The circuit includes an electrically operated compressor which pressurises the fluid, in its gaseous form, thus causing the refrigerant gas to heat up. The hot pressurised gas is then circulated through a condenser, within which it condenses to a liquid, though still under high pressure. This causes the condenser itself to generate heat, which may be recovered to drive domestic heating and hot water systems. From the condenser, the high pressure liquid refrigerant is circulated to an expansion valve, which has the effect of lowering the pressure of the liquid refrigerant so as to promote evaporation. The low pressure liquid refrigerant is then circulated to an evaporator, where it evaporates into a gas, absorbing heat from the evaporator's surroundings as it does so. The gaseous refrigerant then returns to the compressor, and the cycle repeats.

The use of heat pumps for heating domestic or commercial buildings has increased significantly in recent years, due to environmental concerns over more conventional energy sources such as fossil fuels. Energy efficiency and long term running costs are other factors which make heat pump technology attractive. Nevertheless, the use of heat pump installations for domestic purposes has thus far failed to achieve the full potential which this technology offers, for a number of reasons.

Firstly, attempts are often made to connect heat pumps to existing domestic water systems and heating systems using conventional radiators. Such systems are generally inefficient when run at the lower operating temperatures necessitated by the use of a heat pump. The heat pump therefore tends to be relegated to the role of auxiliary heat supply, and is used to ‘top-up’ the heat supply from a conventional boiler, rather than fully replacing it.

An energy efficient heating installation which addresses this problem is disclosed in the applicant's co-pending UK Patent Application No. 09 19636.1, published as GB 2,475,243. The sound-attenuating housing of the present invention is particularly suitable for accommodating a heat pump for use in such a heating installation.

Secondly, heat pumps lose efficiency when the ambient temperature of the heat source medium falls below about 5° C.—around the temperature of an average winter's day in the UK. Thus, the heat pump performs inefficiently in conditions when it is needed most, again leading to heat pumps being used to ‘top-up’ rather than replace conventional heat sources. In addition to the loss in efficiency at ambient temperatures, it is also necessary for anti-freeze additives such as glycol to be added to the refrigerant fluid in the closed circuit. These anti-freeze additives can cause corrosion of components and thus reduce the working life of the heat pump.

A modified heat pump and heat pump installation which exhibits decreased losses in efficiency at low ambient temperatures, and does not require the use of anti-freeze additives—and so addresses the above identified problems associated with operating heat pumps at low ambient temperatures—is disclosed in the applicant's co-pending UK Patent Application No. 10 10759.7. The sound-attenuating housing of the present invention is particularly suitable for accommodating a heat pump for use in such a heating installation.

A particular feature of the heat pump installation disclosed in the applicant's co-pending UK Patent Application No. 10 10759.7 which serves to address the problems associated with operating heat pumps at low ambient temperatures, is that the heat pump is intended to be located within a building to be heated (for example, in a loft space, basement, or utility room), rather than externally thereof as is conventional. Since the interior of the building will generally be at a higher temperature than the exterior when heating is required, locating the heat pump within the building provides further protection against the operating temperature of the heat pump falling below 5° C.

Locating the heat pump within a building necessitates greatly improved sound attenuation, as compared to heat pumps intended for location externally of a building, due to the sound levels generated by the compressor during operation. The present invention seeks to address this requirement by providing sound-attenuating housing suitable for accommodating a heat pump intended to be located in an internal space (loft, basement, utility room etc.) of a building to be heated.

Although the sound-attenuating housing of the present invention has been developed particularly for accommodating a heat pump, it is envisaged that the housing may also be utilised for the accommodation of other mechanical devices where sound-attenuation is required. It should also be understood that the scope of the present invention encompasses both sound-attenuating housing suitable for accommodating a heat pump therein, and a sound-attenuated heat pump assembly comprising a heat pump located within such sound-attenuating housing.

According to a first aspect of the present invention there is provided sound-attenuating housing for a heat pump, said housing comprising:

-   -   a base chassis, upstanding walls surrounding said base chassis,         and a top adapted to engage with said upstanding walls, thereby         to form an enclosure for a heat pump;     -   a first sub-chassis provided within the enclosure, and mounted         on said base chassis via anti-vibration mounts; and     -   a second sub-chassis provided within the enclosure, and mounted         on said first sub-chassis via anti-vibration mounts;     -   wherein said second sub-chassis forms a mounting surface for a         heat pump compressor, and said first sub-chassis forms a         mounting surface for other components of said heat pump.

The top may desirably be removably engagable with the upstanding walls in order to facilitate access to the heat pump components for maintenance. Alternatively, and particularly for the sound-attenuated heat pump assembly embodiments of the present invention, the top may be permanently fixed to the upstanding walls thereby providing a sealed unit.

As described above, the second sub-chassis forms a mounting surface for a heat pump compressor, whilst the first sub-chassis forms a mounting surface for other components of said heat pump. Said other components will typically comprise a condenser, an expansion valve and an evaporator. Where the heat pump is an air source heat pump, said other components will typically further comprise a fan. The arrangement of the compressor being mounted on the second sub-chassis and the other components being mounted on the first sub-chassis is preferably achieved by constructing the second sub-chassis with a substantially smaller surface area than that of the first sub-chassis.

The anti-vibration mounts by means of which the second sub-chassis is mounted on the first sub-chassis, serve greatly to attenuate sound levels transmitted from the compressor, by effectively isolating the compressor from the other components of the heat pump and from the structural elements of the enclosure (that is, the base chassis, the upstanding walls, and the top), and so preventing vibrations caused by the operation of the compressor being transmitted to said other components and structural elements. Similarly, the anti-vibration mounts by means of which the first sub-chassis is mounted on the base chassis serve to attenuate sound levels transmitted from the other components of the heat pump, by effectively isolating said other components from the structural elements of the enclosure, and so preventing the transmission of vibrations caused by the operation of said components. Each sub-chassis thus effectively forms a floating island, which is not in direct contact with the other sub-chassis or with the structural elements of the enclosure. The second sub-chassis is effectively doubly isolated from the structural elements of the enclosure, reflecting the fact that the majority of the sound levels generated by a heat pump during operation originate from the compressor.

The anti-vibration mounts are preferably formed of rubber. Most preferably, the second sub-chassis is mounted on the first sub-chassis via four anti-vibration mounts; and the first sub-chassis is mounted on the base chassis via four anti-vibration mounts. To further enhance the sound attenuating properties of the housing of the present invention, the mounting surface for the compressor on the second sub-chassis may itself be, or be provided with, further anti-vibration mounts, with four again being the most preferred number of said anti-vibration mounts.

In a preferred embodiment of the present invention, the underside of the base chassis is provided with further anti-vibration mounts, externally of the enclosure, for mounting said housing within a building. Again, most preferably four such anti-vibration mounts are provided. The housing may be mounted, via said anti-vibration mounts to any convenient fixing point on a floor or wall of any internal area of a building, such as a basement or utility room. Alternatively, the housing may conveniently be located within an outbuilding. It is preferred however that the housing should be located in a loft space, and to this end, the housing preferably further comprises mounting brackets adapted to receive loft joists. Most preferably, the base chassis is mounted, via said further anti-vibration mounts, on said mounting brackets.

The structural elements of the enclosure are preferably at least partially, and more preferably entirely, lined with acoustic dampening foam or sound mass barrier foam. It is also preferred that, at least one of, and more preferably each of, the base chassis, the first sub-chassis and the second sub-chassis is also lined with acoustic dampening foam or sound mass barrier foam. In a currently preferred embodiment of the present invention, each structural element of the enclosure is lined with acoustic dampening foam having a thickness of at least 50 mm, and each chassis is lined with sound mass barrier foam having a thickness of at least 12 mm.

The housing preferably further comprises a dividing wall arranged at least partially to surround the second sub-chassis, thereby to isolate a heat pump compressor mounted thereon from other heat pump components mounted on the first sub-chassis. The isolation of the compressor from the other heat pump components prevents the transmission of vibrations to said other components during operation of said compressor, thus further reducing the sound levels emitted by a heat pump located within the housing. The dividing wall is also preferably lined with acoustic dampening foam or sound mass barrier foam, with the latter being more preferred.

So as further to reduce the transmission of vibrations between components of a heat pump located within the housing, said housing preferably further comprises flexible connectors to permit fluid connection to and from said heat pump components. The flexible connectors are adapted to permit connection of said heat pump to a domestic hot water and/or central heating system.

Each of the structural elements of the enclosure, each chassis, and the dividing wall, are each preferably formed from a steel plate panel having a thickness of at least 1.2 mm.

The intended location of preferred embodiments of the sound-attenuating housing of the present invention within a loft space makes the use of air source heat pumps particularly suitable for use in heating installations incorporating said housing. In such embodiments, one of the upstanding walls, or the top, of said housing preferably comprises an air inlet. More preferably, said upstanding wall, or said top, comprising the air inlet is further adapted to house, or be associated with, a fan to drive air into the housing.

In such embodiments, one of the upstanding walls, or the top of the housing is preferably further adapted to comprise an air outlet. Said air inlet and said air outlet may desirably be located in opposed upstanding walls. The first sub-chassis may desirably have a mounting surface for a heat pump evaporator located adjacent said air outlet.

As described above, the scope of the present invention encompasses a sound-attenuated heat pump assembly comprising a heat pump located within such sound-attenuating housing.

Therefore, according to a second aspect of the present invention there is provided a sound-attenuated heat pump assembly comprising:

-   -   sound-attenuating housing as hereinbefore described; and     -   a heat pump, comprising a compressor, a condenser, an expansion         valve and an evaporator, mounted within the enclosure of said         housing;     -   wherein the compressor is mounted on the second sub-chassis of         the housing, and the condenser, the expansion valve and the         evaporator are mounted on the first sub-chassis of the housing.

In a preferred embodiment of sound-attenuated heat pump assembly according to the second aspect of the present invention:

-   -   the sound-attenuating housing comprises an air inlet and an air         outlet;     -   the heat pump is an air source heat pump;     -   said heat pump assembly further comprises a fan, mounted in or         adjacent said air inlet; and     -   the evaporator is mounted adjacent the air outlet.

In tests, the sound-attenuated heat pump assembly has been found to be considerably quieter than conventional commercially available heat pumps, emitting sound levels of around 46 dB, said sound measurements being taken from within a building in which the heat pump assembly is installed. By comparison, conventional commercially available heat pumps for domestic use typically emit sound levels in the region of 60 dB.

In order that the present invention may be more clearly understood, a preferred embodiment thereof will now be described in detail, though only by way of example, with reference to the accompanying drawings, in which:

FIG. 1 shows an exploded side view of a preferred embodiment of sound-attenuating housing for a heat pump, according to the present invention; and

FIG. 2 shows an exploded plan view of the sound-attenuating housing of FIG. 1.

It should be understood that the following description refers equally to the sound-attenuating housing according to the first aspect of the present invention, and to the sound-attenuated heat pump assembly according to the second aspect of the present invention.

Referring simultaneously to FIGS. 1 and 2, there are shown, respectively, exploded side and plan views of sound-attenuating housing, generally indicated 10, for housing a heat pump, according to the present invention. The housing 10 has a base chassis 11, with upstanding opposed side walls 12, 13, and upstanding opposed end walls 14, 15 surrounding said base chassis 11. A top 16, adapted removably to engage with the upstanding walls 12-15, completes an enclosure for a heat pump.

As can best be seen from FIG. 1, a first sub-chassis 17 is mounted, via a first set of anti-vibration mounts 18, on the base chassis 11. Similarly, a second sub-chassis 19 is mounted, via a second set of anti-vibration mounts 21, on the first sub-chassis 17. Further, the base chassis 11 is itself mounted, via a third set of anti-vibration mounts 22, on mounting brackets 23, for locating the housing 10 in a suitable location within a building. Each mounting bracket 23 may be adapted to receive or engage with a loft joist, thereby enabling the housing 10 to be conveniently located within the loft of a building, and/or may be provided with rubber feet 24.

Referring now to FIG. 1, the second sub-chassis 19 forms a mounting surface for a heat pump compressor 25. Other heat pump components (condenser, expansion valve and evaporator) are not illustrated in FIG. 1 but should be assumed to be present, and mounted on the first sub-chassis 17. The sound-attenuation of the present invention is primarily concerned with the compressor 25 rather than said other components, since it is the compressor 25 which generates the noise which the present invention seeks to reduce. As can be seen in both FIGS. 1 and 2, the compressor 25 is mounted on the second sub-chassis 19 using a fourth set of anti-vibration mounts 26, located at the corners of the compressor 25.

As can also be seen, the second sub-chassis 19 is considerably smaller than the first sub-chassis 17. Thus, with the compressor 25 mounted on the second sub-chassis 19 and the other heat pump components mounted on the first sub-chassis 17, the compressor 25 is doubly isolated from the base chassis 11—via two sets of anti-vibration mounts 18, 21. This serves to reduce the vibrations transmitted from the compressor 25 to the base chassis 11, and so to attenuate the sound levels emitted by the housing.

Sound levels are attenuated further by the provision of a dividing wall 27 arranged so as partially to surround the second sub-chassis 19, and thus further isolate the compressor 25 from the remainder of the housing 10, and the other heat pump components therewithin. The dividing wall 27 is provided on its outer surface with a lining 28 comprising 12 mm of high density sound mass barrier foam. A similar lining 28 is provided on the upper surface of the first sub-chassis 17. Acoustic dampening foam, having a thickness of 50 mm is used to provide a lining 29 on: the inner surface of the dividing wall 27; the lower surface of the first sub-chassis 17; and the inner surfaces of the top 16, and each of the walls 12-15.

Referring now to FIG. 2, this shows an arrangement of particular use when the housing 10 is used to accommodate an air source heat pump. As can be seen, in this embodiment the first side wall 12 is provided with an air inlet 31, having a fan 32 associated with said air inlet 31 housed in said first side wall 12. The opposed second side wall 13 has an air outlet 33, and has the heat pump evaporator 34 located at or adjacent said air outlet 33. The fan 31 is arranged to drive air into the housing 10 and over the evaporator 34, to enable the heat pump to extract heat from said air.

The provision of all of the above described sound-attenuating features greatly reduces the vibrations transmitted from the compressor 25 to the exterior of the housing 10 during operation of the heat pump, and so greatly reduces the sound levels emitted by the heat pump assembly. As such, the heat pump assembly may be tolerably located within the interior of a building, thus prolonging the life of the unit by avoiding the need for corrosive anti-freeze chemicals to be used, increasing the efficiency of the unit at ambient temperatures of below 5° C., and facilitating recovery of heat from within the building, thus further increasing efficiency. 

1. Sound-attenuating housing for a heat pump, said housing comprising: a base chassis, upstanding walls surrounding said base chassis, and a top engaging with said upstanding walls, thereby to form an enclosure for a heat pump; a first sub-chassis provided within the enclosure and provided with first anti-vibration mounts, said first sub-chassis being mounted on said the base chassis via said first anti-vibration mounts; and a second sub-chassis provided within the enclosure and provided with second anti-vibration mounts, said second sub-chassis being mounted on the first sub-chassis via said second anti-vibration mounts; wherein the second sub-chassis forms a mounting surface for a compressor of a heat pump, and the first sub-chassis forms a mounting surface for other components of said heat pump.
 2. The sound-attenuating housing as claimed in claim 1, wherein the base chassis is provided with third anti-vibration mounts located externally of the enclosure, for mounting said housing within a building.
 3. The sound-attenuating housing as claimed in claim 2, wherein the base chassis is provided with mounting brackets, said base chassis being mounted on said mounting brackets via the third anti-vibration mounts, wherein said mounting brackets are arranged to receive loft joists, thereby to enable said housing to be mounted in a loft of a building.
 4. The sound-attenuating housing as claimed in claim 1, wherein the enclosure is at least partially lined with a foam selected from the group consisting of acoustic dampening foam and sound mass barrier foam.
 5. The sound-attenuating housing as claimed in claim 1, wherein at least one of the base chassis, the first sub-chassis and the second sub-chassis is lined with a foam selected from the group consisting of acoustic dampening foam and sound mass barrier foam.
 6. The sound-attenuating housing as claimed in claim 1, further comprising a dividing wall arranged at least partially to surround the second sub-chassis, thereby to isolate a compressor of a heat pump mounted thereon from other components of said heat pump mounted on the first sub-chassis.
 7. The sound-attenuating housing as claimed in claim 6, wherein the dividing wall is lined with a foam selected from the group consisting of acoustic dampening foam and sound mass barrier foam.
 8. The sound-attenuating housing as claimed in claim 1, wherein said housing comprises acoustic dampening foam having a thickness of at least 50 mm.
 9. The sound-attenuating housing as claimed in claim 1, wherein said housing comprises sound mass barrier foam having a thickness of at least 12 mm.
 10. The sound-attenuating housing as claimed in claim 1, further comprising flexible connectors to enable fluid connection of components of a heat pump mounted within the enclosure to and from a domestic hot water heating system.
 11. The sound-attenuating housing as claimed in claim 1, wherein the base chassis, walls, top, first sub-chassis and second sub-chassis are each formed from steel plate panels having a thickness of at least 1.2 mm.
 12. The sound-attenuating housing as claimed in claim 6, wherein the dividing wall is formed from a steel plate panel having a thickness of at least 1.2 mm.
 13. The sound-attenuating housing as claimed in claim 1, wherein said housing is for an air source heat pump, and wherein one component selected from the upstanding walls and the top, comprises an air inlet.
 14. The sound-attenuating housing as claimed in claim 13, wherein said one component selected from the upstanding walls and the top, comprising the air inlet, is further adapted to house a fan to drive air into the housing.
 15. The sound-attenuating housing as claimed in claim 13, wherein one component selected from the upstanding walls and the top, comprises an air outlet.
 16. The sound-attenuating housing as claimed in claim 15, wherein the first sub-chassis has a mounting surface for a heat pump evaporator located adjacent the air outlet.
 17. A sound-attenuated heat pump assembly comprising: the sound-attenuating housing as claimed in claim 1; and a heat pump, comprising a compressor, a condenser, an expansion valve and an evaporator, mounted within the enclosure of said housing; wherein the compressor is mounted on the second sub-chassis of the housing, and the condenser, the expansion valve and the evaporator are mounted on the first sub-chassis of the housing.
 18. The sound-attenuated heat pump assembly as claimed in claim 17, wherein: the sound-attenuating housing is for an air source heat pump; and wherein one component selected from the upstanding walls and the top comprises an air inlet, and one component selected from the upstanding walls and the top comprises an air outlet; the heat pump is an air source heat pump; said heat pump assembly further comprises a fan, mounted in or adjacent said air inlet; and the evaporator is mounted adjacent the air outlet.
 19. The sound-attenuating housing as claimed in claim 4, wherein the enclosure is entirely lined with a foam selected from the group consisting of acoustic dampening foam and sound mass barrier foam.
 20. The sound-attenuating housing as claimed in claim 6, wherein each of the base chassis, the first sub-chassis and the second sub-chassis is lined with a foam selected from the group consisting of acoustic dampening foam and sound mass barrier foam. 